Mars Aligned - Ions, Methane, and Exploration

[redliox]

Condensing and refining all my 'Aligned ideas here and will focus on this thread.

Once again I express the need for being conservative in flying to Mars, but also tempered with enlightened goals like long term exploration and sustainability, not a mere flags-and-footprints or a technological-and-political quagmire like the STS or ISS.  Reading through the many ideas expressed here gives further enlightenment; many of the refinements I suggest here are a result of your suggestions.  What I've concluded is that most of the technologies suggested for Mars are all indispensable; the only true limitation beyond R&D is, frankly, when to deploy them and that is where being practical comes into play.

Speeches and formalities out of the way, down to business...

Let's look at what NASA has been thinking about:
1) Asteroids are falling out of favor, but the SEP behind ARM may yet survive.
2) Orbiting Mars before landing seems favored.
3) Deimos and Phobos slowly garnering attention, partly as better targets for an ARM-Mars path.
4) Congress wants to prioritize Mars versus programs like ARM or Earth Science, which in their eyes detracts from space exploration.

So NASA's getting nudged away from asteroids but not quite toward Moon;  Mars is the unified goal.  We have enough technology to get beyond LEO but few for directly landing on Mars.  Still, Curiosity and Mars 2020 show we are starting to land sizeable (but not crew-ready) payloads directly on Mars.  What could we do prior to humans on Mars?

Improvise with what we got.

If we look at what we have available (in propulsion in this example), we currently have:
-Cryogenic H2/O2 upper stages (Centaur, soon ICUS & EUS)
-Hypergollic upper stages & onboard propulsion
-Solar Electric Propulsion (DS2, Dawn, Boeing 702 sats)

What we further need is:
-CH4/O2 rockets (Blue Origins' B-4 engine may remedy this in near future)
-ISRU of CH4/H2/O2 on Mars (MOXIE on 2020 may establish O2, but still need CH4 & perhaps H2)
-Aerocapture & General Improvement of EDL (bigger heatshields, some-kinda-flaps to extend said-shields, powered descent, and pintpoint landing)

Of the needed tech, CH4 rocketry should be available soon (via Blue Origin and ULA, perhaps SpaceX).  Life support and rad shielding obvious to merit, but if the ISS serves its mission we'll be prepared by 2030.  Considering how Curiosity survived direct descent, in principle we could aerocapture at Mars with current means but human life shouldn't be gambled until perfected (along with EDL furthermore).  On top of that, without complete ISRU any mission, orbital or landed, will require a propellant parade; if cryogenic, we'd risk boiling off mass without (unproven) long-term cooling systems...which would turn a simple stage into an expensive spacecraft in development.

What elements we have to work with, currently and the near future, are SLS, Orion, commercial capsule (Dragon 2, ect.), the larger commercial rockets (Delta 4, Falcon Heavy [perhaps Ariane 5, Vulcan]), and then hypergolic and electric propulsion systems.  Not completely ideal, since we will be currently bound to supply from Earth, but I believe it is possible.

Before, and in tandem with, human flights, there should be cargo flights embarking directly to Mars.  These would do two functions: test the unproven tech needed and deliver (obviously) cargo (chiefly to the surface, but serviceable satellites another).  I will get to these in a second post tomorrow.

The first crewed flight could indeed be orbital, but without dragging either Orion (which is effectively useless beyond the Moon) or a 'propellant parade' of stages to be dropped.  A Deep Space Habitat and a SEP tug could do the job - considering there'll never be a  budget to launch literally a dozen SLSs (or two dozen smaller commercial rockets likewise) just to deliver fuel pods.

The breakdown of both delta-v and mass during such an orbital flight:

Earth Departure Operations
LEO to EML 1 -  4 km/s
TMI from EML 1 - 1.5 km/s

Mars Orbital Operations
MOI - 1.5 km/s
Deimos - 1.1 km/s
Reserve - 0.5 km/s
ETI - 1.9 km/s
Total: 5 km/s

Earth Return Operations
EML 1 Capture - 2 km/s
Earth return - 0.7 km/s
Total: 2.7 km/s

Needed Delta-v: 9 km/s


Exploration Upper Stage
Dry Mass: 12 metric tons
Wet Mass: 120 metric tons
Propellant: 108 (H2/O2 - ISP 450)
Delta-v: 10.1 km/s

Mars Transit Habitat
Hab-30 mt/Kick Stage (Dry) 6.3 mt
Propellant 9.6 metric tons (N204/MMH - ISP 336)
Total Mass: 45.9 metric tons
Delta-v: 0.7 km/s

Interplanetary Ion Tug ITIT
Total Dry Mass: 30 metric tons
Total Wet Mass: 80 metric tons
Total Propellant: 50 metric tons (Xenon - ISP 3000)
Delta-v: 28.8 km/s

MTH+ITIT+EUS
Dry Mass: 137.9
Total Wet Mass: 245.9
Propellant: 108 (H2/O2 - ISP 450)
Delta-V: 2.5 km/s


Orbital Flight w/ MTH/ITIT/EUS+Orion

1) MTH docks with ITIT/EUS in LEO
2) Transfer Orbit - Mass Before 245.9 mt / Mass After 137.9 mt
Propellant consumed: 108 mt (H2/O2 - ISP 450)
Delta-v: 2.5 km/s
3) EUS jettisoned
4) EML1 - Mass Before 125.9 mt / Mass After 119.5 mt
Propellant consumed: 6.4 mt (Xenon - ISP 3000)
Delta-v: 1.5 km/s
5) Orion dock with MTH to transfer crew at EML1
6) TMI - Mass Before 119.5 mt / Mass After 110 mt
Propellant consumed: 9.5 mt (Xenon - ISP 3000)
Delta-v: 2.4 km/s
7) MOI - Mass Before 110 mt / Mass After 104 mt
Propellant consumed: 6 mt (Xenon - ISP 3000)
Delta-v: 1.6 km/s
8) Deimos - Mass Before 104 mt / Mass After 100 mt
Propellant consumed: 4 mt (Xenon - ISP 3000)
Delta-v: 1.1 km/s
9) Reserve - Mass Before 100 mt / Mass After 98.1 mt
Propellant consumed: 1.9 mt (Xenon - ISP 3000)
Delta-v: 0.5 km/s
10) ETI - Mass Before 98.1 mt / Mass After 91 mt
Propellant consumed: 7.1 mt (Xenon - ISP 3000)
Delta-v: 2.2 km/s
11) EM1 Capture - Mass Before 91 mt / Mass After 83.5 mt
Propellant consumed: 7.5 mt (Xenon - ISP 3000)
Delta-v: 2.5 km/s
12) Orion docks with MTH to return crew to Earth

Bear in mind, I am not an advocate of electric propulsion (indeed the actual advocates here would note I've criticized it heavily).  However, I did the math using EUS and hypothetical methalox stages, the later carrying 100 tons of methalox apiece, and while a EUS+2 methalox stages could get a crew to Mars, there was no way it could get a crew and the return fuel there too.  Using current technology with minimal R&D, the most effective combination to expect is H2/O2 stage+SEP.  In 5 years we could add CH4/O2 stages, but not the ISRU to make it long-term effective.  Not advocating anything, just stating what we can improvise with.

An all SEP-setup I wouldn't recommend actually, but on the very first flight to Mars orbit (and Deimos) it may be what to expect, especially without a magical-ever-frozen-cryogenic stage.  Given a conjunction class mission that will be in the area of 1000 days...frankly time will be in abundance...and while in orbit waiting on the ion drive to shuffle between MOI, Deimos operations, synchronous orbit, and possibly Phobos, the crew will constantly be in view of Mars exactly like the ISS crew has of Earth on it's month-long visits.  Time enough to be busy with remote Martian science, astronomy, and PR interviews to classrooms on Earth.

What I do recommend is using an MTH to shuttle between EML and areosynchronous orbit with a kick from hydrolox from Earth (through EUS or its descendants) and methalox from Mars for the outbound.  Inbound to each planet, to quote Patrick Star (of all characters, yes), they "gently float back down."  In other words, chemical thrust for the outbound, ion thrust on arrival.  Given the choice between slow SEP, super-cool liquids failing to stay cool over a few months, or a fiery hell-ride of aerocapture...well you tell me which is practical.  As for "why aren't you using both systems simultaneously?" well mass is why; if we don't have a super-chiller fuel tank the next choice is hypergolic...and the only reason that is listed with the MTH specs is to allow for maneuvers at EML and Deimos ill-suited for slow SEP.  Hypergolic is dead weight from low isp whereas cryogenic 'spoils' too quickly.  Best to use the speed of chemical rockets near their fuel supply.

While I am chiefly explaining an initial Mars orbital mission, I will mention crew landers before closing this initial post.  Their function would be dependent on ISRU, whereas the MTH is independent (hence how it could be used well before ISRU setup).  Like cargo landers, they would be delivered by aerocapture but placed into orbit essentially empty, awaiting the MTH to dock.  On the surface, like any ISRU architecture, they refuel and return to orbit and the MTH.  They would be single stage, reusable vehicles that draw on Martian fuel.  There could be a disposable ascent vehicle used instead, but in the long term a SSTO reuseable lander would be optimal.  Furthermore, a large version could double as the methalox stage the MTH would use to leave Mars.

Quite a bit to post...but I have been thinking thoroughly on this architecture.  I expect a few debates, but I have tried to error on the heavier side with matters like delta-v to give margin...not to mention drawing on SEP gives more margin for the same propellant mass.  More details to come, especially on Martian elements.

[KelvinZero]

Pet peeve: long term propellant storage is often implied as difficult, like violation of thermodynamics difficult. I think this is an absurd meme spawned because propellant depots are politically inconvenient for SLS, even though any long term BEO plans assume significant propellant storage.

Even passive systems are meant to bring boiloff down to a few percent per year in a high orbit. Then you just add some active cooling. If you can't reliquify a very slow trickle of cold gas in an environment where oxygen lines freeze by accident then the notion of ISRU to aquire - then liquify and store - tons of hot gasses is absurd and the fact we have been doing this on earth for a century or so is absurd.

[redliox]

Pet peeve: long term propellant storage is often implied as difficult, like violation of thermodynamics difficult. I think this is an absurd meme spawned because propellant depots are politically inconvenient for SLS, even though any long term BEO plans assume significant propellant storage.

Even passive systems are meant to bring boiloff down to a few percent per year in a high orbit. Then you just add some active cooling. If you can't reliquify a very slow trickle of cold gas in an environment where oxygen lines freeze by accident then the notion of ISRU to aquire - then liquify and store - tons of hot gasses is absurd and the fact we have been doing this on earth for a century or so is absurd.

If it is possible then that means, during initial assembly, the MTH and the ITIT could each launch with an EUS.  The first EUS would be spent in a transfer orbit, but the second could be held onto up through EML (1 or 2), and once the crew boards they could be injected onto a swift transit (perhaps even as low as 5 months).

Even with passive systems, you are still talking multiple launches and dealing with the annoying mass problem prior to ISRU freeing up the system.  Furthermore, any SLS launch not involving Orion is best spent sending a large hab/cargo lander to Mars itself.  The chiller option would help, especially if ion tugs are employed between LEO and the Moon, but it shouldn't be treated as a crutch.

[gbaikie]

I think NASA should mothball or some other option [other than crashing ISS into atmosphere] of no longer having the need of 3 billion per year cost of ISS, by 2025.
And think should start a major Mars exploration program by 2025.

In the time before 2025, NASA should develop operational use of depots in Orbit [LEO- KSC inclination].
And should start a major lunar exploration program which will be ended by 2025.
The lunar exploration start with robotic program [lander/orbitors] which intended to determine if and where there is minable water deposit in the lunar polar regions. And prior to 2025, have few manned mission
to lunar surface which will bring back well preserved lunar samples.
And major lunar program does not include building a lunar base, nor mining lunar water.
And the total cost should be about 40 billion and roughly 1/2 is manned and 1/2 is robotic or non manned.
Generally speaking the non crewed exploration will require more years than crewed missions. And crew missions will tend to explore the moon more thoroughly in a given location and in shorter period of time than compared to robotic missions.
So around 2025, in terms of human spaceflight, NASA will have 3 programs: ISS and lunar- which are ending, and Mars which is beginning.
And prior to 2025 one will continue the scheduled/planned Mars mission and add more robotic  mission in regards to Mars in preparation for crew going to Mars. And they should be related to landing sites selection for crewed mission to Mars.
As far as Mars moons, it seems we should send robotic mission to evaluate potential use of moons related to crew exploration of Mars. Not sure when, but of course before sending crew or making too many plans in terms of mars bases.
And at 2025, would have operational depot at LEO and/or at high earth orbit. And most likely not have commerical lunar water mining, though could have the beginning steps of such operation beginning as result positive results of lunar exploration. But waiting such things which may or may not occur is unrelated
to the mars exploration program. And perhaps something like the result of Mars moon's exploration could [though perhaps unlikely] could have more commercial mining potential. Or who knows what else might be possible by that point in time. But seems that if lunar exploration in beginning appears to being giving negative results, that NASA may need to re-evalate lunar exploration. And it's focus should related to exploration related to starting new markets in space. As that is sole purpose of exploring the Moon.
Mars is similar though probably a longer project- or it's purpose of determine if human settlement are viable option related to Mars. And is more possible if there is lunar markets which exist.

[redliox]

As promised, I'll now elaborate on the cargo and robotic elements.

Compared to crews, that are effectively cradled, robots can be handled a little more forcefully directly.  While there will be a significant orbital element to crew delivery, the robotic elements will be primarily surface-based.  The whole focus will be to create a significant, self-sustaining base with the minimal number of flights as possible.  This will happen in two forms:

1) Pathfinders - 66% scale testbeds
2) Base Habs - Full scale habitats

The Pathfinders would consist of 2 types of payloads: a ISRU lander with rovers and a SEP satellite with docking and refueling capability; the landers would mass about 20 metric tons while the satellites around 30.  They would be optimized for launch aboard something other than SLS, namely Falcon Heavy into LEO.  From there, the SEP sats spiral the whole Pathfinder out to Mars.  Prior to arrival, lander and sat split - the sat spiraling down to synchronous orbit while the lander aerocaptures prior to landing.

Elaborating on the Pathfinder lander, it would chiefly be a fuel factory with two MER-sized ultility rovers.  The lander would produce methane and oxygen, the later both in Sabatier reactions and solid-oxide electrolysis; furthermore there could be water electrolysis to experiment with getting hydrogen out of Martian soil.  The rovers would primarily plow the area around the lander to turn it into a landing field and eventually a base site.  Otherwise they would map the area optically supplemented by subsurface radar and neutron spectroscopy; shoving dirt around and taking pictures would be their sole job.  In the end, the lander's function would be to create a fuel supply and safe haven for a Mars base.

The Pathfinder satellite has two primary tasks with some long-term secondary functions.  First, it would loft itself and an accompanying lander from LEO to Mars, settling into a synchronous orbit above the future base site.  When it's tug task is complete, the same SEP is used for station-keeping.    Then it other primary task comes into play: communication relay, which is could do with both traditional radio and laser communication, the former acting as a backup in case the later fails (since lasers do eventually burn out).  It would be meant as a long-term comsat, largely thanks to the SEP; the visiting MHTs could deliver a ton of fuel to refuel the sats, enabling them to last as long as the Hubble (perhaps even upgrading them in similar fashion, if budgets are generous enough); I would presume to give the sats at least refueling capability if nothing more.  A final long-term function would be a docking node; not so much to make them space stations, but so any loitering spacecraft have an open garage to sit at; coupled with the SEP this would be useful.  One end of the satellite would have three passive ports while the sides and aft end dominated by solar arrays, com equipment, and the SEP thrusters.  Modest (but not small) package with multiple uses.

The Base Habs would be 30 mt landers that function as the core of a Mars base.  As their name implies, they'd primarily be a habitat, but solar arrays, at least an unpressurized crew rover, and oxygen ISRU would be included with this.  They would arrive in the same manner as the Pathfinders, by aerocapture then propulsive landing.  One advantage their landing would have is the landed Pathfinder could have a guiding beacon, and the space cleared by the utility rovers (even if only a square kilometer) would provide both a visual target and landing zone.

All together, I would suggest flying two sets of Pathfinders (2 landers+2 sats) and three Base Habs to a single site adjacent to a prominent equatorial region; this could include Valles Marineris or Meridiani Planum for examples.  I advocate focusing instead of numerous sites for several reasons:

1) Avoid spreading resources (and limited temperamental Congressional funding) too thinly
2) Build a solid base with more redundancy and sustainability
3) Thoroughly investigate one region deeply and not at a glance
4) By 2030 (if not already) the database from probes will allow selection of a worthwhile permanent base site

Long-range rovers would allow more than local science.  Even if only one base is ever made, if the base is placed expertly scientists could visit many varied sites.  Referring to V.M. and M.P. for instance, a rover from a base in the canyon's center could eventually drive to Noctis Labyrinthus in the West or the channels emptying into Chryse Planitia out East and for the Planum sampling the varying craters and small channel systems.

As for the Pathfinder comsats, while two might not suffice for a GPS network this could be bolstered by complementary cubesats.  Their orbital positions, just like satellites over Earth, could be adjusted to widen their range; this could reasonably be as much as 66% of the planet while keeping base contact - even a circum-Martian expedition would draw use from this.  Otherwise giving them the ability to dock and hold a crew lander between flights may be preferable to wasteful dumping or leaving them unattended and frozen on Mars.

At least hypothetically more could be done; this could range from adding more hab modules to ISRU from the Martian moons.  I would suggest a solid approach, establishing a capable base within reach yet interesting for both science and PR.  I will further add, much of this scheme is open; the Pathfinders are intentionally smaller than the Mars Habs or MTH so that commercial or international partners could assist, and likewise a crew lander could take many forms more creative than I could conceive.  I would like to think what I've laid out here would amount to a solid bridgehead for bigger plans.

[KelvinZero]

About asteroids are falling out of favor.. The nearest I can see are hints of a DSH in high lunar orbit with international cooperation, which would be silly not to do if we take the asteroid route anyway. It just needs more money so is likely to happen second.

So Im thinking this MTH should also be this DSH. All these pieces won't emerge at once so it is just as interesting to think about what we do in the meantime. I think we can gain excellent confidence for a mars orbit mission just sitting in high lunar orbit, but without attention to our politicians we could end up with a lunar DSH that somehow proves irrelevant to Mars ambitions which would be a great pity.

[redliox]

So Im thinking this MTH should also be this DSH. All these pieces won't emerge at once so it is just as interesting to think about what we do in the meantime. I think we can gain excellent confidence for a mars orbit mission just sitting in high lunar orbit, but without attention to our politicians we could end up with a lunar DSH that somehow proves irrelevant to Mars ambitions which would be a great pity.

Unsure if you imply support or discontent for a DSH.

The reason I support a DSH/MTH is two-fold:
1) NASA seems convinced significant breathing room is needed for Mars flights; considering these will be month/year-long endeavors there is a point.
2) An orbital Mars mission will need something better than Orion to do the job, both in habitat volume and propulsive capability; we all know Orion's really a cheap Moon ship.

[spacenut]

I agree with using Falcon H to do a lot of Mars preparation work. 

1) Reusable large SEP tugs, that can be refueled by say a Falcon 9 or compatible rocket in LEO for round trip to Mars. 

2) Disposable landers which carry and land:

a) Landing area preparation equipment
b) Fuel manufacturing equipment.
c) Robotic electric powered graders, excavators, dump trucks for ISRU work.
d) Solar power equipment.
e) Habitats
f) A Mars GPS and satellite communication system in orbit prior to colonization.
 
50 ton total payloads of this equipment with disposable landers can be delivered by Falcon Heavies to each returning SEP tug along with a Falcon 9 refueling on the tug. 

This could keep Falcon Heavies busy launching and if other nations or other companies wish to participate, they either refuel the tug, or launch something for the Tugs to take to Mars.  That could insure them a ride to Mars when the MCT's are built. 

I personally believe the BFR and MCT should not exceed pad 39a and 39b's capability (12 million lbs thrust) so as to be able to not only use Kennedy, but also the Texas site.  Even if it means say 75 tons to Mars instead of 100 tons for a practical more robust reusable system.  However, Falcon Heavies could do a lot of prep work on Mars 4-8 years prior to MCT's coming on line. 

[KelvinZero]

Im a big supporter of a DSH.
I was just noting it should be thought of as independent of the propulsion. The DSH is an excellent component to build early and start accruing confidence in for multiyear missions, long before heading for Mars.

[spacenut]

What does DSH and MTH?  Can't figure out what they mean?  Thanks.

[Pipcard]

Deep Space Habitat and Mars Transit Habitat.

[Darkseraph]

Pet peeve: long term propellant storage is often implied as difficult, like violation of thermodynamics difficult. I think this is an absurd meme spawned because propellant depots are politically inconvenient for SLS, even though any long term BEO plans assume significant propellant storage.

Even passive systems are meant to bring boiloff down to a few percent per year in a high orbit. Then you just add some active cooling. If you can't reliquify a very slow trickle of cold gas in an environment where oxygen lines freeze by accident then the notion of ISRU to aquire - then liquify and store - tons of hot gasses is absurd and the fact we have been doing this on earth for a century or so is absurd.

I don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.

 My pet peeve is people counting their MCT's before they hatch. I believe mega rockets will return to being relevant when we're sending thousands of people to space every year...but we're not doing that for a long time and even multiples of current flight rates can be supported with systems that lift no more than 50 tons to LEO. I was personally amazed that those who slung mud at Ares/SLS for years completely changed tune with SpaceX saying about doing a rocket in that class, even though most of the arguments against the former system equally apply to any system SpaceX would field. I could be wrong about this and there are details to the MCT that make it a scalable system that has other commercial uses, but I've heard nothing of that nature yet. For expected near terms missions to Mars and the Moon, I overall think it makes more sense to do a single core reusable methane rocket that lifts about the same payload as Falcon Heavy, can support wider payloads; that can be later scaled up as demand increases. But hey, it's not my company!

[spacenut]

At least SpaceX is shooting for completely reusable systems.  SLS is not.  It could have been.  It was suggested way back then that it should have fly back liquid boosters.  The core should have used the old J2 plug nozzle technology with about 4 of this making a ring to return the core.  Then you could have a completely reusable system at say 70-75 tons to LEO.  Then add a possible single J2 plug nozzle 3rd stage and you have your 120 tons or so to LEO and completely reusable system.  As much money as they have thrown around, that was possible. 

[redliox]

There could be a possibility for reuseable vehicles, depending on their function.

For starters, the more passive the vehicle's function, the better its odds for longevity.  The MTH and Pathfinder sats, after launch and basic deployment (solar arrays, radio dishes) would be quiet vehicles.  They would fire either maneuvering or ion thrusters, but no major moving parts, fried super engines and heat shields,  or exposure to events like reentry or debris strikes in LEO (moreso since MTH would only return to EML-1/2 from Mars and never closer).  Indeed, I would expect the MTH to be reused numerous times with modest refuels.  In the case of the sats, the least that should be done for them is to refuel their xenon tanks every few years, at best treat them like a com-themed Hubble; indeed for some of Hubble's earliest missions they actually succeeded in replacing parts that hadn't been intended to be replaceable.

The crewed lander, acting as a Martian shuttle, could be the next avenue of reuseability.  Except when the lander doubles as a permanent surface hab, even modern schemes still dump the vehicle.  However, as the space shuttle itself and the failed X-33 remind us, they're not easy.  How much easier this would be at Mars is further debatable.  However, if we are to reuse it and store it somewhere, Mars orbit would be better to avoid cold damage from the red planet.  I would heavily recommend some kind of SSTO lander/shuttle, but I could only guess how it could be developed - but this could be an avenue taken up by ESA or commercial entities in place of NASA to lessen issues.  The Orion capsule/cabin may have use, but its weight may fit like a box in a round hole here...which is why the Orion's only role in my plans is crew delivery and retrieval from near the Moon.

Inevitably there will be some disposable components.  However, I believe this could be limited strictly to launch vehicles and booster stages.  Anything that carries crew should be reused, but I wouldn't give as much priority to reuseable Mars boosters as opposed to something like ISRU...which would supply the 90% of mass that fills the rocket to begin with.  Two exceptions I'll make to this: a future Mars tanker shuttle and a reusable first stage on Earth.  SpaceX will eventually perfect landing the stages back, and that alone will help considerably (so long as the engines and tanks remain intact).  The Mars tanker could come in two forms: a shuttle that carries fuel from Mars to a stage or pod in orbit, or carries the fuel and is the booster stage that sends crew back to Earth.  I favor the later, since it would be easier just to transfer the entire load once, on Mars, rather than multiple trips and worrying about a leaky fuel line in orbit.  I would prioritize just getting the crew up to synchronous orbit with ISRU for a start, but in the long run getting chemical propulsion on both ends of a Mars trip.  Whether or not the booster stages should be reused is trivial during base construction and initial footsteps (~10 years) but after a Mars base that can supply fuel is established, THEN advocate total reusability.

[redliox]

At least SpaceX is shooting for completely reusable systems.  SLS is not.  It could have been. 

Not much point in crying over spilt milk, but because it will be a one-shot HLV, here's my policy on using it for Mars: save it for the big stuff.

Here's the breakdown on my schemes' vehicles and masses:

Pathfinder Satellite
Total Dry Mass: 20 metric tons
Total Wet Mass: 30 metric tons
Propellant: 10 metric tons (Xenon - ISP 3000)
Delta-v: 32.3 km/s

Pathfinder Lander
Total Dry Mass: 17 metric tons
Total Wet Mass: 20 metric tons
Propellant: 3 metric tons (N204/MMH - ISP 336)
Delta-v: 0.5 km/s

Mars Transit Habitat - MTH
Hab-30 mt/Kick Stage (Dry) 6.3 mt
Propellant 9.6 metric tons (N204/MMH - ISP 336)
Total Mass: 45.9 metric tons
Delta-v: 0.7 km/s

Interplanetary Ion Tug - ITIT
Total Dry Mass: 30 metric tons
Total Wet Mass: 80 metric tons
Total Propellant: 50 metric tons (Xenon - ISP 3000)
Delta-v: 28.8 km/s

Mars Surface Habitat - MSH
Total Dry Mass: 42 metric tons
Total Wet Mass: 50 metric tons
Total Propellant: 8 metric tons (CH4/O2 - ISP 380)
Delta-v: 0.6 km/s


For better or worse, we will have to expect an Orion/SLS flight twice for one Martian mission - first to deliver and the second to retrieve the crew from the MTH.  That puts the number at once a year at least.

As can be seen though, most of my vehicles are sized for 50 tons, with only ITIT above this (and its mass is a gross estimate; it could possibly be lighter and retain its performance).  Both types of habitats, surface and transit, are within the threshold for a FH, as is the combined Pathfinder package.  The Pathfinders would definitely fly by FH, using SEP from LEO to Mars all the way.  For the habs and ITIT there are two routes to take:

Falcon Path:
1 MTH
3 MSH
2 ITIT
6 FH

SLS Path:
1 MTH
3 MSH
1 ITIT
4 SLS

On the Falcon path, it would be assumed the ITIT is downsized to match ~51 mt, with the difference being a reduction in xenon.  Two ITITs, one for the MTH (with the humans aboard) and the second for the MSH.  The lessened propellant would be inconsequential to the MSH - the ITIT's job is boosting to Hoffman orbit speed and returning to Earth while the MSH aerocapture at Mars.  For the MTH, the ITIT would first boost the pair all the way to EML from LEO (not a small chore); the same Orion that delivers the crew might need to bring some xenon with it - but given the capacity of the SLS (especially with the Block 1B's EUS) this may be minor.  More time is needed for all the habitats to reach Mars, but feasible with some TLC to the crew's ITIT specifically.

The SLS would send the MSHs on a Mars Direct-style course; even at the heavier 50 mt (versus 'Direct's ~25 mt) they would be flying on reasonably swift paths at over 4 km/s out of LEO (the Hoffman minimum is 2.2 from LEO), no ITIT required.  A MTH+ITIT could fit together on SLS, but would only receive a boost slightly better than a Geostationary Transfer Orbit.  The ITIT could easily shove the MTH the rest of the way, and indeed is nominally configured this way.  The only refuel needed for ITIT would be after the returning crew link with the 2nd Orion at EML.

So, in short, we could choose between a 2 SLS/6 FH combo or a 6 SLS.  These flights would be distributed over the course of 6 years, and exclude the Pathfinders' launches; 3 surface habs delivered to fully form the base and an orbital mission conducted.

A crewed surface mission would face a similar selection, with a crew lander & ITIT with 2 FHs or a single SLS flying the crew lander alone; in both cases the lander aerocaptures into orbit.  The crew fly totally independently in the previous MTH-ITIT to rendezvous in synchronous Mars orbit.

I slightly favor the SLS for fewer flights, but the FH I would press for use all the same whenever possible.  Otherwise the true decider is radiation tolerance of the Van Allen belts - the MTH-ITIT will have to endure moderate exposure even on an SLS path, but the EUS boost would hasten the trip.  No humans would be aboard during this moment, only for the EML rendezvous via Orion.

[spacenut]

I would prefer argon for SEP tugs vs xenon.  Argon is in earths atmosphere and is far more abundant.  It is also about 4-5% of Mars atmosphere.  It could be extracted from Mars and launched up to fuel a SEP tug for it's trip back to earth, at least eventually.  Xenon is very rare and with all the moving around between earth and Mars, to me it makes sense in the long run to use argon. 

[redliox]

I would prefer argon for SEP tugs vs xenon.  Argon is in earths atmosphere and is far more abundant.  It is also about 4-5% of Mars atmosphere.  It could be extracted from Mars and launched up to fuel a SEP tug for it's trip back to earth, at least eventually.  Xenon is very rare and with all the moving around between earth and Mars, to me it makes sense in the long run to use argon.

I've actually heard xenon is a common byproduct of oxygen liquidation here on Earth.  Argon probably would work just as well, but xenon is the heaviest and a lot of the other choices for electric propulsion can be toxic metals, like mercury for one.  Given the low consumption rate of EP fuel to begin with there might not be much demand to refuel it at Mars, but then again that could be added to the long term goals alongside complete reusability.

[spacenut]

I was just thinking with the high concentration of argon on Mars, while we are cracking CO2 and making fuel, argon could be separated and pressurized to fly back up to be able to refuel a SEP tug system.  Wouldn't take a large rocket to take off in the 40% gravity well to dock and pressurize a tug.  This might be a long term solution since SEP tugs might be carrying cargo to Mars on a regular basis after a colony is established and growing.  Even dry food not grown on Mars would be a cheap bulk item to be carried to Mars such as wheat, corn, soybeans, sugar, or rice, which take more acreage to grow than just vegetables.  Argon, being plentiful on Mars might be cheaper to extract from Mars atmosphere launched into Mars orbit, than launched into earth orbit, or to an L2 gateway. 

[RanulfC]

I don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.

The problem is that argument is circular in that because they are not "off-the-shelf" (and if you refer to the ACES/Depot studies it nearly is) we should not put them on the "critical path" yet at the same time nothing that is NOT on the "critical path" is being funded so they will by default, never be "off-the-shelf" so they should never be on the critical path...

This is exactly why we're here now. We choose a "goal" for which we develop a "critical path" but then specifically do not engage in any infrastructure or equipment development outside of that path but a lot of development within that path to achieve the goal. And pretty much ONLY the goal. This process has proved a failure at sustainment ever single time it has been followed, yet we continue to do the same thing over and over again and expect a different result. (This is the definition of crazy I will note)

My pet peeve is people counting their MCT's before they hatch. I believe mega rockets will return to being relevant when we're sending thousands of people to space every year...but we're not doing that for a long time and even multiples of current flight rates can be supported with systems that lift no more than 50 tons to LEO. I was personally amazed that those who slung mud at Ares/SLS for years completely changed tune with SpaceX saying about doing a rocket in that class, even though most of the arguments against the former system equally apply to any system SpaceX would field. I could be wrong about this and there are details to the MCT that make it a scalable system that has other commercial uses, but I've heard nothing of that nature yet. For expected near terms missions to Mars and the Moon, I overall think it makes more sense to do a single core reusable methane rocket that lifts about the same payload as Falcon Heavy, can support wider payloads; that can be later scaled up as demand increases. But hey, it's not my company!

Being honest Ares/SLS is what it is; A government launcher built to government specifications, not "exactly" a mouse/elephant relationship but dang close. MCT has at least suggested changes to the normal BFR paradigm with on-orbit refueling and some other suggestions which were all "rejected" (not off-the-shelf so not on the critical path and really NOT considered because they actively or were inferred to interfere with said "critical path" specifications) by the government. But to be fully honest you have to be aware of and consider the goals of each vehicle. BFR/MCT is aimed at putting a specific amount of payload (be it people or equipment) on the surface of Mars. SLS is aimed at putting 130 tons into LEO and that's it for the "official" reason for existence.

FH and an FH-class LV simply won't meet the requirements of either, though personally I think your closer to right, the point would be that it can't meet any of the targets presented as is. My personal belief is that we need higher flight rates to LEO and on-orbit infrastructure with dedicated space-to-space transfer vehicles using efficient in-space propulsion systems rather than launching huge missions on one-shot expendable launchers or surface to surface reusable vehicles. But the people with the actual money and control think differently and will have their way it seems.

Randy

[redliox]

I don't think they are impossible...I do think we don't have them off-the-shelf, so putting them on the critical path makes programs around them much more expensive and easier to cancel. I absolutely support their development and I believe in the long run that they are necessary, that the mega-rocket cargo cult has to go away to make human expansion into space viable, even when there are lulls in government support.

The problem is that argument is circular in that because they are not "off-the-shelf" (and if you refer to the ACES/Depot studies it nearly is) we should not put them on the "critical path" yet at the same time nothing that is NOT on the "critical path" is being funded so they will by default, never be "off-the-shelf" so they should never be on the critical path...

This is exactly why we're here now. We choose a "goal" for which we develop a "critical path" but then specifically do not engage in any infrastructure or equipment development outside of that path but a lot of development within that path to achieve the goal. And pretty much ONLY the goal. This process has proved a failure at sustainment ever single time it has been followed, yet we continue to do the same thing over and over again and expect a different result. (This is the definition of crazy I will note)

Regarding fuel depots, unless you count storage tanks attached to the ISRU on Mars (or Luna and perhaps Deimos/Phobos) I don't think they're honestly necessary.  I say that on the ground of cutting out the middleman.  Send down a lander, fill it up, put it back in orbit, and use it like a booster stage to push the vehicle back home.  You end up doing a similar pattern with a depot spread out over a dozen flights.  Follow something like a Mars Direct-Semi-Direct path and keep it simple.

The only orbital infrastructure I suggest under 'Aligned is a couple comsats that double as a parking space.  Otherwise with a fuel efficient system like EP (or future high-isp drives or EM drives) there's less need for fuel in deep space.  The gas station doesn't need to be in orbit itself.  If you're going to put up infrastructure, put it near the source of fuel.  This is another reason concentrating on a single strong base initially helps.